Patients who need to use inhalers, such as pMDI devices, need to monitor their inhaler usage, and regulators of medicines have begun to require that some method of dose counting is included into the inhaler. Dose counters (providing a precise count of the number of doses remaining) and dose indicators (providing an indication of the number of doses remaining) for inhalers are known.
In most dose counters and dose indicators, the display is indexed each time the inhaler device is used and a dose is delivered, e.g. from a metering valve of the inhaler where the inhaler is a pMDI. It is particularly important that dose counters and dose indicators do not undercount the number of dispensed doses as, in extreme cases, the patient may rely on the display shown on the pMDI device to receive life-saving medication. Note that the term ‘dose’, as used herein, includes individual deliveries of medication formulation that in multiple make up a single therapeutic dose.
In dose counters or dose indicators, it may be acceptable for advancement of the display to be triggered (initiated) before or after the dose has been delivered, provided that the patient cannot dispense a dose without triggering it. Many dose counters and/or dose indicators are complex, requiring a number of small mechanical parts, which may increase cost, may lead to difficulties in assembly, and may require tight dimensional tolerances.